The use of thick film conductors in hybrid microelectronic components is well known in the electronics field. Such materials are usually comprised of a dispersion of finely divided particles of a noble metal, noble metal alloy or mixtures thereof and inorganic binder, both dispersed in an organic medium to form a pastelike product. The consistency and rheology of the paste is adjusted to the particular method of application such as screen printing, brushing, dipping, extrusion, spraying and the like. Such pastes are usually applied to an inert substrate such as alumina by screen printing to form a patterned layer. The patterned thick film conductor layer is then fired to volatilize (e.g., "burn off") the organic medium and sinter both the inorganic binder, which is typically a glass or a glass-forming material, and the finely divided particles of noble metals, noble metal alloys or mixtures thereof. Firing temperatures for such pastes are usually about 600.degree.-900.degree. C.
In addition to the electrical conductivity properties which the fired conductive layer possesses, the fired layer needs to adhere firmly to the substrate on which it is printed and that layer needs to be capable of accepting solder. Solderability is a very desirable property because of the necessity of connecting the conductive pattern with other components of the electronic system in which it is to be used, e.g., resistor and capacitor networks, resistors, trim potentiometers, chip resistors, chip capacitors, chip carriers and the like.
Customer needs and expectations continually increase for commercial thick film pastes. The requirements of high adhesion and high solderability become increasingly difficult to simultaneously meet. The inorganic binder phase that is included in a thick film conductor composition for the purpose of adhesion can interfere with solder wetting. Thus, techniques and compositions that can raise soldered adhesion while minimizing degradation to conductor solderability are particularly valuable.